There are a lot of topics to cover and a lot of resources I use to get to some solutions.
Enumeration
linpeas – Very powerful tool to enumerate your target. Just download the script and execute it on your target machine
Cryptography
Ciphey – A new and very powerful tool I found for quickly solving cryptography challenges.
CyberChef – The most powerful tool to convert from hex, binary, BaseXX and so on
ROT13 – I use it for ROT rotations for most of the time but this online tool contains a lot more stuff worth using
Vigenere Solver – If you have to crack a vigenere code without owning a key, this tool can help you out
quipquip – To crack substitution ciphers
Hashcracking
CrackStation – Helps cracking most of the hashes very quickly
MD5Hashing – If CrackStation doesn’t help, try this page to crack all sorts of hashes
Privilege escalation
GTFOBins – Here you can find a huge collection of binaries for a lot of situations to gain root privileges
pentestmonkey – A collection of reverse shells for the most commonly used programming languages
RSA
factordb – In case you need to factorize for decrypting a RSA key
Alpertron – Sometimes I’m using this tool as well and it’s worth checking out
Misc
URL de-/enoder – Awesome tool if you have to deal with URL encoded format
WaybackMachine – A website everyone needs to discover some old websites (very useful for some CTF challenges)
MarCorei7 